Cross flow baffle for a steam generator

ABSTRACT

A steam generator having a U-shaped tube bundle and a baffle and tube support which has circulation holes drilled in a selective pattern to promote cross flow across the hot leg of the tube bundle to eliminate chemical hideout and poor flow distribution.

United States Patent Byerley et a1.

[451 Feb. 25, 1975 CROSS FLOW RAFFLE FOR A STEAM GENERATOR Inventors:Wilbur M. Byerley; Robert R.

Bennett, both of Tampa, Fla.

Westinghouse Electric Corporation,

Assignee:

Pittsburgh, Pa.

Filed: Apr. 24, 1973 Appl. No.: 354,031

11.8. C1 122/32, 122/34, 165/159, 165/161 Int. Cl. F221) 1/04 Field ofSearch; 122/32, 34; 165/134, 159, 165/161 [56] References Cited UNITEDSTATES PATENTS 3,147,743 9/1964 Romanos 122/32 3,706,301 12/1972Penfield,.lr 122/32 Primary Examiner-Kenneth W. Sprague Attorney, Agent,or Firm-F. .1. Baehr, Jr.

[57] ABSTRACT 6 Claims, 7 Drawing Figures CROSS FLOW RAFFLE FOR A STEAMGENERATOR BACKGROUND OF THE INVENTION This invention relates to steamgenerators for nuclear power generating plants and more particularly toa cross flow baffle disposed adjacent to tube sheet to eliminatechemical hideout and improve flow distribution.

Nuclear steam generators, like-fossil fuel steam generators, have beensubjected to tube failures. Recent compilation of data for numerousinstallations has shown a tendency for tube failures to occur within aregion adjacent the center of the hotleg of the steam generators tubebundle.

It is hypothesized that a treatment void is created at the center of thehotleg adjacent the tube sheet due to buoyancy effects which subject thetube to cyclic temperature excursions which produce thermal stressesthat result in a premature tube failure. Thus, by eliminating thesevoids the tube life can be appreciably extended.

SUMMARY OF THE INVENTION Among the objects of this invention may benoted the provision of a baffle which will channel the flow of thesecondary fluid toward a central portion of the hotleg of the tubebundle to eliminate chemical hideout and improve flow distribution overthe hotleg thus minimizing premature tube failure.

In general, a vapor generator, when made in accordance with thisinvention, comprises a shell portion, a tube handle having a pluralityof tubes disposed within the shell portion, a wrapper disposed withinthe shell so as to generally enwrap'the tube bundle, a tube sheetdisposed on one end of the tube handle, ahead portion cooperativelyassociated with the shell and tube sheet,

. a primary fluid inlet nozzle for supplying primary fluid to the insideof the tubes, a secondaryfluid inlet nozzle for supplying secondaryfluid to the inside of the shell and the outside of the tubes, and abaffle disposed parallel to the tube sheet and cooperatively associatedwith the wrapper so that the influent secondary fluid sweeps cross thetube sheet as it flows between an area between the baffle and the tubesheet. The baffle has a plurality of tube holes through which the tubepass and a plurality of circulation holes through which the influentsecondary fluid flows. The circulation holes are disposed in a pluralityof zones, 21 first zone adjacent the center of the baffle whichgenerally has a maximum number and size of circulation holes togenerally form a maximum amount of open area for the flow of secondaryfluid through the first zone and a second zone disposed adjacent thefirst zone, the second zone having circulation holes arranged to formsubstantially less than the maximum amount of open area for the flow ofsecondary fluid therethrough.

BRIEF DESCRIPTION OF THE DRAWING The objects and advantages of thisinvention will become more apparent from reading the following detaileddescription in connection with the accompanying drawings, in whichcorresponding reference characters indicate corresponding portionthroughout the drawings, and in which:

FIG. I is a sectional view of a steam generator having a pre-heater anda baffle made in accordance with this invention;

FIG. 2 is a section taken on line II-Il of FIG. 1;

FIG. 3 is a partial sectional view of a steam generator without apre-heater and having a baffle made in accordance with this invention;

FIG. 4 is a sectional view taken on line IV-IV of FIG. 3;

FIG. 5 is an enlarged partial sectional view showing an arrangement offlow holes;

FIG. 6 is an enlarged partial sectional view showing an alternatearrangement of flow holes; and

FIG. 7 is an enlarged partial sectional view showing still anotheralternate arrangement of flow holes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsin detail, FIG. 1 shows a steam or vapor generator 1 having a verticalshell portion 3 and a plurality of U-shaped tubes 5 forming a tubebundle 7 which is disposed within the shell 3. The shell has a lowerportion 9 having one diameter, an upper portion 1 1 having a largerdiameter, and a frustoconical portion 13 serving as a transition memberbetween the upper and lower portion 11 and 9, respectively. The lowerportion 9 of the shell 3 is enclosed by a sphericalhead portion 15. Thehead portion 15 has an integral tube sheet I7 which receives the ends ofthe U-shaped tubes 5. A dividing plate 19 separates the head into twogenerally equal compartments 21 and 23. The inlet compartment 21, theone on the left as shown on the drawings, has an inlet nozzle 25 forprimary fluid and the outlet compartment 23, the one on the right asshown on the drawings, has an outlet nozzle disposed therein, however,the outlet nozzle is not shown. A sleeve or wrapper portion 27 enwrapsthe tube bundle and forms an annular chamber 29 between the wrapper 27and the shell 3. A pre-heater portion 31 is disposed adjacent the tubesheet 17 on the coldleg portion of the tube bundle 7, the portion shownon the right in the drawings. The pre-heater 31 is an enclosed chamberformed by a portion of the wrapper 27, a bottom .circular closure plate33 disposed adjacent and parallel to the tube sheet, an upper closureplate 34 disposed parallel to the bottom closure plate, and a verticalclosure plate 35 extending between the bottom and upper clo-.

sure plates 33 and 34, respectively. A secondary fluid or feed waterinlet nozzle 37 is disposed in the shell adjacent the pro-heater and hasa sleeve 41 which directs the inlet water to the pre-heater and impactplate 43 which directs the inlet flow downwardly and prevents the highvelocity inlet secondary fluid from impinging on the tubes. A pluralityof horizontal baffles 45 are so disposed within the pre-heater to causethe influent secondary fluid to follow asinuous path as it flowsupwardly to an outlet portion 47, which discharges the pre-heatedsecondary fluid into the annular chamber 29. A horizontal battle andtube support 51 which is disposed adjacent and parallel to the tubesheet, generally extends over the hotleg portion of the tube bundle 7and has a plurality of tube holes 53 and circulation or flow holes 55disposed in prearranged pattern.

The end of the wrapper 27 adjacent the tube sheet 7 has a plurality ofnotches 57 so disposed to direct the secondary fluidso that it sweepsacross the tube sheet 17 prior to flowing upwardly through thecirculation holes 55 and then along the outer surface of the tubes notcontained within the pre-heater. Some of the notches 57 are providedwith adjustable flow gates 59 which are adapted to change the open areaof the notches to adjust the flow of the pre-heated secondary fluidacross the tube sheet 17.

The wrapper 27 generally parallels the shell and flairs outwardly alongwith the transition portion 13 and has a domed end enclosure 60 disposedin the lower portion of the upper portion 11 of the shell 3. The domedenclosure 60 and the wrapper 27 thus forms a chamber 61 above the tubefor collecting steam or vapor produced by the steam generator. The upperportion 11 of the shell is closed by an elliptical head portion 63. Asteam or vapor outlet nozzle 65 is centrally disposed in the ellipticalhead portion 63 and provides a discharge port for vapor produced in thesteam generator. Two diametrically opposed man-ways 67 provide access tothe interior of the upper portion of the shell which houses two separatemoisture or liquid separators 69 and 71. The first separator 69 is acentrifugal type separator and comprises a plurality of riser tubes 73in communication with the chamber 61 and extends upwardly from the domedend portion 60 of the wrapper 27. The riser tubes 73 have swirl vanes 75disposed therein. The swirl vanes 75 extend radially from a centrallydisposed hub portion 77 which is disposed adjacent the upper end of theriser tube 73. A closure plate 79 is disposed slightly above the upperend of the riser tubes 73 and has orifices 81 which register with theriser tubes 73. Collars 83 extend through the orifices 81 and extenddownwardly therefrom. Sleeves 85 encircle the riser tube and extend fromthe closure plate 79. The lower end of the sleeve 85 is disposed abovethe domed enclosure 60 providing a lower discharge port. The upper endsof the sleeves have tangential discharge ports 87 disposed adjacent theclosure plate 79.

The second moisture separator 71 comprises two groups of hook and pocketvane-type or chevron separators disposed in parallel, one group beingdisposed above the other. The hook and pocket vane-type separators 71have drip-leg 89 depending therefrom, the lower end of the drip-leg 89has a seal cup 91 connected thereto and the discharge from the seal cups91 joins with the moisture from the centrifugal separators and flowsinto the annular chamber 29.

As shown in FIG. 2, the baffle 51 is generally semicircular shaped andhas circulation holes 55 disposed in zones Z1, Z2, and Z4. Each zoneincorporates circulation holes 51 which are a particular size and arearranged to provide an open area which is a percentage of the maximumallowable open area that can be obtained and still provides a matrixwhich will support the tubes 3.

Zone Z,, the first zone, is disposed adjacent the cen' ter or in thecentral portion of the baffle 51 and generally contains the maximumnumber and size of circulation holes to generally provide a maximumamount of open area for the flow of secondary fluidsthrough thecirculation holes 55 disposed in zone 2;.

Zone 2;, the second zone, is disposed adjacent and generally encircleszone Z Zone 2 generally has circulation holes 55 arranged to formsubstantially less than the maximum amount of open area for the flow ofsecondary fluids through the circulation holes contained in zone Z Thezone Z preferably provides an open area of about 20 to 50 percent of themaximum open area that could be provided. Such a zone may be formed bydeleting a certain number of circulation holes 55 as shown in FIG. 6 orby reducing the size of the circulation hole 55 as shown in FIG. 7 or bya combination of deleting circulation holes and reducing their size.

A peripheral zone 2,, comprises a band of circulation holes 55 and isdisposed adjacent the peripheral edge of the baffle 51. Zone Z containscirculation holes 55 arranged to generally provide the maximum open areafor the flow of secondary fluid, as shown in FIG. 5.

FIGS. 3 and 4 show a portion of a steam generator which does not have apre-heater. Therefore the baffle 51' adjacent the tube sheet isgenerally circular.

The second fluid inlet nozzle 37 directs the influent secondary fluid tothe annular chamber 29 between the wrapper 27 and the shell 3. Theinfluent secondary fluid flows downwardly through the port 57 and sweepsthe tube sheet 17 and then flows upwardly through the circulation holes55 in the baffle 51.

The circulation holes 55 are arranged in a plurality of zones Z Z Z andZ each with a predetermined number of circulation holes 55 of varioussize to provide zones having different percentages of open areas throughwhich the secondary fluid can flow.

Zone Z generally has circulation holes arranged to generally provide themaximum amount of open area through which the secondary fluid can flowand is generally disposed in the central portion of the baffle 51. ZoneZ is disposed adjacent zone Z, and generally encircles zone Z Zone Zgenerally has circulation holes 55 arranged to generally provide about20 to 50 percent of the maximum amount of open area that could beprovided for the flow of secondary fluid therethrough.

Zone Z generally has circulation holes 55 arranged to generally provideabout 0 percent to 30 percent of the maximum amount of open area thatcould be provided for the flow of secondary fluid therethrough.

Providing a baffle plate 51 or 51', as hereinbefore described, with aplurality of zones having various amounts of open area advantageouslychannels influent secondary fluid to areas which have been particularlysusceptible to premature failure to reduce chemical hideout and improvethe flow distribution of the secondary fluid to substantially reducepremature failure of the tube adjacent the tube sheet.

What is claimed is:

1. A vapor generator comprising a shell portion,

a tube bundle having a plurality of tubes disposed within said shellportion,

a wrapper disposed within said shell so as to generally enwrap said tubebundle,

a tube sheet disposed on one end of the tube bundle a head portioncooperatively associated with said shell and tube sheet,

a primary fluid inlet nozzle for supplying primary fluid to the insideof said tube,

a secondary fluid inlet nozzle for supplying secondary fluid to theinside of said shell and the outside of said tubes,

a baffle disposed parallel to said tube sheet and cooperativelyassociated with said wrapper so that at least a portion of the secondaryfluid sweeps across said tube sheet and flows between an area betweensaid baffle and said tube sheet,

said baffle having a plurality of tube holes through which the tubespass, said holes embracing said tubes and said baffle having a pluralityof circulation holes through which at least a portion of the secondaryfluid flows,

said circulation holes being disposed in a plurality of zones,

a first zone adjacent the central portion of said baffle, said firstzone generally having a maximum number and size of circulation holes togenerally form a maximum amount of open area for the flow of secq d yflu dthet mwu ht a second zone disposed adjacent and generallyencircling said first zone, said second zone having circulation holesarranged to form substantially less than the maximum amount of open areafor the flow of secondary fluid through said second zone.

2. A steam generator as set forth in claim 1, and further comprising athird zone adjacent said second zone said third zone having flow holesarranged to form substantially less open area than formed in said secondzone.

3. A steam generator as set forth in claim 2, wherein the second zonegenerally encircles the first zone and the third zone generallyencircles the second zone.

4. A steam generator as set forth in claim 2 and further comprising afourth zone generally forming a narrow band adjacent the perimeter ofthe baffle, said fourth zone having circulation holes generally arrangedto provide the maximum amount. of open area for the flow of thesecondary fluid therethrough.

5. A steam generator as set forth in claim 1, wherein the tube bundleshas U-shaped tubes forming a hotleg portion and a pre-heater is disposedover a portion of the cold leg portion of the tube bundles and thebaffle is generally semi-circular and is disposed over the hot legportion of the tube bundle and the first zone is generallysemi-circular.

6. A steam generator as set forth in claim 5, and further comprising athird zone generally a narrow band adjacent the perimeter of the baffle,said third zone having circulation holes arranged to generally providethe maximum amount of open area for the flow of said secondary fluidtherethrough.

1. A vapor generator comprising a shell portion, a tube bundle having aplurality of tubes disposed within said shell portion, a wrapperdisposed within said shell so as to generally enwrap said tube bundle, atube sheet disposed on one end of the tube bundle a head portioncooperatively associated with said shell and tube sheet, a primary fluidinlet nozzle for supplying primary fluid to the inside of said tube, asecondary fluid inlet nozzle for supplying secondary fluid to the insideof said shell and the outside of said tubes, a baffle disposed parallelto said tube sheet and cooperatively associated with said wrapper sothat at least a portion of the secondary fluid sweeps across said tubesheet and flows between an area between said baffle and said tube sheet,said baffle having a plurality of tube holes through which the tubespass, said holes embracing said tubes and said baffle having a pluralityof circulation holes through which at least a portion of the secondaryfluid flows, said circulation holes being disposed in a plurality ofzones, a first zone adjacent the central portion of said baffle, saidfirst zone generally having a maximum number and size of circulationholes to generally form a maximum amount of open area for the flow ofsecondary therethrough, and a second zone disposed adjacent andgenerally encircling said first zone, said second zone havingcirculation holes arranged to form substantially less than the maximumamount of open area for the flow of secondary fluid through said secondzone.
 2. A steam generator as set forth in claim 1, and furthercomprising a third zone adjacent said second zone said third zone havingflow holes arranged to form substantially less open area than formed insaid second zone.
 3. A steam generator as set forth in claim 2, whereinthe second zone generally encircles the first zone and the third zonegenerally encircles the second zone.
 4. A steam generator as set forthin claim 2 and further comprising a fourth zone generally forming anarrow band adjacent the perimeter of the baffle, said fourth zonehaving circulation holes generally arranged to provide the maximumamount of open area for the flow of the secondary fluid therethrough. 5.A steam generator as set forth in claim 1, wherein the tube bundles hasU-shaped tubes forming a hotleg portion and a pre-heater is disposedover a portion of the cold leg portion of the tube bundles and thebaffle is generally semi-circular and is disposed over the hot legportion of the tube bundle and the first zone is generallysemi-circular.
 6. A steam generator as set forth in claim 5, and furthercomprising a third zone generally a narrow band adjaceNt the perimeterof the baffle, said third zone having circulation holes arranged togenerally provide the maximum amount of open area for the flow of saidsecondary fluid therethrough.